Linnaeus’ thermometer

After his appointment as Professor of
medicine in 1741 at Uppsala University, Linnaeus began to
restore and extend the botanical garden which had been created
in the township Svartbäcken in Uppsala by professor
Olof Rudbeck as early as 1655. In this project Linnaeus worked
together with the famous architect Carl Hårleman. The
whole garden got a completely new orientation more to east
and west, a baroque design and a new orangery with two annexes
inspired from Linnaeus’ time in Holland.

For his new orangery with its
annexes, the solarium (sun house) and the vaporarium
(steam house), Linnaeus required a functional thermometer
in order to control the environment in the best possible
way for his valuable plant material.

However, Linnaeus’ interest in
the climate requirements of plants can be found already
in 1737 and 1739 in his reports on his observations
with a Fahrenheit thermometer from George Clifford's
garden in Holland. This is long before he was appointed
Professor of medicine and Head of the botanical garden
at Uppsala University. In the quite extensive description
of Clifford's garden by Linneus, Hortus Cliffortianus
(1737), there is quite an interesting frontispiece
inserted, rich in allusive details. This is a beautiful
allegorical plate, including many interesting details,
for example the two little boys (putti) at the bottom
of the figure, pointing to a very special thermometer
(Fig. 1).

Fig. 1 Part of Jan Wandelaar's
illustration in Hortus Cliffortianus by Linnaeus (1737).
One of the two putti is holding a thermometer of a surprisingly
modern design.
Photo from The Carolina Library, Uppsala
University.

It is astounding that the design of that
thermometer is already so modern in its general outlines
and that Linnaeus also indicates its importance to control
the cultivation conditions. The thermometer in the frontispiece
with the two putti most likely never existed at that time.
However, we know that about seven years later Linnaeus obtained
a thermometer surprisingly like it from the instrument workshop
of the Royal Swedish Academy of Sciences (KVA) in Stockholm
(Fig. 2).
In this workshop other high-quality technical instruments
for astronomers, geographical surveyors etc were also made.
Some of these instruments may still be seen in Museum
Gustavianum, Uppsala University and in the Observatory
Museum in Stockholm.

The leading maker of scientific instruments
at this time in Sweden was the wellknown Daniel Ekström.
Presumably Linnaeus ordered his mercury thermometer as early
as 1743, so that Ekström was able to deliver the first "linnaeus-thermometer" in
1744. However, this very first thermometer was broken on
its way from Stockholm to the Botanical Garden in Uppsala.
Today we can see in the correspondence between Linnaeus and
the secretary Pehr Elvius of the KVA just how anxious Linnaeus
was to have a second thermometer ready in ample time to give
temperature data to the coming documentation of the newly
restored garden.

The second thermometer arrived in good
condition in the garden in November 1745, and Linnaeus notes
in his letter of thanks to Elvius that it was "very
well made indeed.” Somewhat later, on December 2,
1745, a proud Linnaeus could demonstrate it to the University
Board. The thermometer was a success among the learned gentlemen
and the purchase of the instrument was approved. It may be
noted that among the Board members was a certain professor
M. Strömer who succeeded the late professor A. Celsius
on the chair of astronomy.

Two weeks later Linnaeus’ description
of the garden was published in the paper Hortus Upsaliensis with quite illustrative drawings and Samuel Nauclér
as respondent. Here Linné gives a more comprehensive
description of the renewed and extended botanical garden,
stating its aim and history etc, specially pointing out its
usefulness even for the ordinary society. When describing
the orangery Linnaeus gave this most interesting technical
report:

”since the caldarium (the hot
part of the greenhouse) by the angle of the windows, merely
from the rays of the sun, obtains such heat that the thermometer
often reaches 30 degrees, although the keen gardener usually
takes care not to let it rise to more than 20 to 25 degrees,
and in winter not under 15 degrees...” and
Linnaeus continues in a footnote: ”... our thermometer
shows 0 (zero) at the point where water freezes and 100 degrees
at the boiling-point of water.”

It is thus graded in the same way as
our contemporary thermometer. Besides the pithy physical
description of the Caldarium, it is worth noting that this
is the first time in history *16th of December 1745* that
we are given a temperature report in "modern" celsius-degrees
and that was from the orangery in the Botanical Garden of
Uppsala University, today known as the Linnaeus garden.

Fig. 2 Thermometer made for Linnaeus
in the workshop of the Royal Swedish Academy of Sciences
by Johan Gustav Hasselström (signature IGH) at
the end of the 1770's. Linnaeus’ first thermometer
probably looked just the same.
Photo from The Linnaeus
Museum in Uppsala.

The temperature scale was performed
after the late professor of astronomy Anders Celsius' well
defined natural fixpoints. In his famous work Observationer
om twänne beständiga Grader på en Thermometer
(1742), (Observations about two fixed degrees on a thermometer), he used
the boiling- and freezing-points of water to obtain
his temperature scale after most
careful measurements. In Museum Gustavianum
it is still possible to see one of the thermometers
(de l'Isles' thermometer) which he used
to establish his fix-points. Celsius' own thermometer
instrument with its linear scale was of glass and designed
for more experimental purposes starting with 0° at
the boiling-point (D) and 100° at the freezing-point
(C) of water (Fig. 3).
This implied a practical method
to measure, e.g., weather conditions, with no plus
or minus. Linnaeus however, as a scientist, had the
original Celsius scale turned, so that 0 (zero) was
marked for the freezing-point and 100 for the boiling-point
of water for his instrument (Fig. 2). By that Linnaeus
got a thermometer better suited for biological conditions.
Plants risk to die at 0° C. The celsius-scale,
altered in this way, gives the reading below zero for
minus-degrees and above zero for plus-degrees. But
it also gives a much wider use, as one can even measure
extreme temperatures as, e.g., the meltingpoint of
iron (+1535°C). With Celsius' original thermometer-scale
this would have been quite difficult.

A year later, 1746, another similar thermometer
from KVA's workshop appeared at the department of astronomy.
This is remarkable since the above mentioned professor Strömer
earlier, in the 3rd quarter issue of the Academy Transactions
(KVAH 1745(3)), had strongly recommended a Hauksbee thermometer,
after working together with his brother in law, namely the
instrument maker Daniel Ekström (!!), about the barometer's
influence on the temperature-changes. From 1750 they abandoned
Celsius' original thermometer-scale at the department
of astronomy in favour of the altered celsius-scale.

Linnaeus was also
eager to supply his disciples with the new instrument.
When Pehr Kalm
went to North America in 1747 and Anton
Rolandson Martin to Spitzbergen in 1758 they were both supplied with
this new thermometer.

Another one of Linneus' disciples,
Anders Sparrman, supplemented his original observations
in Fahrenheit-degrees
with the new Celsius-degrees, so that he could
give both readings in his original journal from South Africa.

In Linnaeus’ day a thermometer
was indeed not in everyone's possession. The
price was as much as 30 Swedish copper dalers which
was about a month's salary for a blacksmith,
or the price of a musket. In comparison we may note
that a hunting rifle today costs about 10.000 SEK or
1000 EUR. No wonder Linnaeus was anxious that the University
should approve the purchase. This has then given us
evidence of his great interest in the thermometer also
from a technical point of view by the letters and minutes
that are still preserved today. It is also clear from
them that Linnaeus was the very first to cause a thermometer
to be functionally designed, measuring in degrees Celsius
in the way we are now used to, already in 1744. The
thermometer we use today is thus what you might call
a "Linnaeus-thermometer.” In its growing
triumphal progress throughout the world it has been
called Celsius-novum or just the Swedish thermometer
and in our days the Celsius thermometer.

Once again, it should be stressed
that it is the combination of Celsius' ingenious
method of determining the fixpoints and Linnaeus’ initiative
as to the functional design of the thermometer which
together form the basis of the first thermometer using
modern Celsius degrees (C°).

Fig. 3 Celsius' own glass thermometer
copied from the illustration accompanying his
famous article in KVAH III(3): Tab. VII, Fig.1
(1742). The boiling-point is marked 0 at D and the
freezing-point 100 at C.

Finally, this may also be a good example
of the importance of an open academic research environment
where the free exchange of ideas has its advantages – then
and today.